simplify placeholder validation

src/pretix/base/forms/validators.py

@@ -39,7 +39,7 @@ from django.core.validators import BaseValidator
 from django.utils.translation import gettext_lazy as _
 from i18nfield.strings import LazyI18nString
 
-from pretix.helpers.format import SafeFormatter
+from pretix.helpers.format import format_map
 
 
 class PlaceholderValidator(BaseValidator):
@@ -49,6 +49,12 @@ class PlaceholderValidator(BaseValidator):
     which are not presented in taken list.
     """
 
+    error_message = _(
+        'There is an error with your placeholder syntax. Please check that the opening "{" and closing "}" curly '
+        'brackets on your placeholders match up. '
+        'Please note: to use literal "{" or "}", you need to double them as "{{" and "}}".'
+    )
+
     def __init__(self, limit_value):
         super().__init__(limit_value)
         self.limit_value = limit_value
@@ -60,23 +66,14 @@ class PlaceholderValidator(BaseValidator):
             return
 
         try:
-            SafeFormatter(None).parse(value)
+            format_map(value, {key.strip('{}'): "" for key in self.limit_value}, ignore_missing_keys=False)
         except ValueError:
+            raise ValidationError(self.error_message, code='invalid_placeholder_syntax')
+        except KeyError as e:
             raise ValidationError(
-                _('Invalid placeholder syntax: You used a different number of "{" than of "}".'),
-                code='invalid_placeholder_syntax',
-            )
-
-        data_placeholders = list(re.findall(r'({[^}]*})', value, re.X))
-        invalid_placeholders = []
-        for placeholder in data_placeholders:
-            if placeholder not in self.limit_value:
-                invalid_placeholders.append(placeholder)
-        if invalid_placeholders:
-            raise ValidationError(
-                _('Invalid placeholder(s): %(value)s'),
+                _('Invalid placeholder: {%(value)s}'),
                 code='invalid_placeholders',
-                params={'value': ", ".join(invalid_placeholders,)})
+                params={'value': e.args[0]})
 
     def clean(self, x):
         return x

src/pretix/control/views/event.py

@@ -73,6 +73,7 @@ from i18nfield.utils import I18nJSONEncoder
 
 from pretix.base.channels import get_all_sales_channels
 from pretix.base.email import get_available_placeholders
+from pretix.base.forms import PlaceholderValidator
 from pretix.base.models import Event, LogEntry, Order, TaxRule, Voucher
 from pretix.base.models.event import EventMetaValue
 from pretix.base.services import tickets
@@ -713,11 +714,6 @@ class MailSettingsSetup(EventPermissionRequiredMixin, MailSettingsSetupView):
 class MailSettingsPreview(EventPermissionRequiredMixin, View):
     permission = 'can_change_event_settings'
 
-    # return the origin text if key is missing in dict
-    class SafeDict(dict):
-        def __missing__(self, key):
-            return '{' + key + '}'
-
     # create index-language mapping
     @cached_property
     def supported_locale(self):
@@ -742,7 +738,7 @@ class MailSettingsPreview(EventPermissionRequiredMixin, View):
                     _('This value will be replaced based on dynamic parameters.'),
                     s
                 )
-        return self.SafeDict(ctx)
+        return ctx
 
     def post(self, request, *args, **kwargs):
         preview_item = request.POST.get('item', '')
@@ -760,13 +756,17 @@ class MailSettingsPreview(EventPermissionRequiredMixin, View):
                     with language(self.supported_locale[idx], self.request.event.settings.region):
                         try:
                             if k.startswith('mail_subject_'):
-                                msgs[self.supported_locale[idx]] = format_map(bleach.clean(v), self.placeholders(preview_item))
+                                msgs[self.supported_locale[idx]] = format_map(bleach.clean(v), self.placeholders(preview_item), ignore_missing_keys=False)
                             else:
                                 msgs[self.supported_locale[idx]] = markdown_compile_email(
-                                    format_map(v, self.placeholders(preview_item))
+                                    format_map(v, self.placeholders(preview_item), ignore_missing_keys=False)
                                 )
                         except ValueError:
-                            msgs[self.supported_locale[idx]] = _('Invalid placeholder syntax: You used a different number of "{" than of "}".')
+                            msgs[self.supported_locale[idx]] = '<div class="alert alert-danger">{}</div>'.format(
+                                PlaceholderValidator.error_message)
+                        except KeyError as e:
+                            msgs[self.supported_locale[idx]] = '<div class="alert alert-danger">{}</div>'.format(
+                                _('Invalid placeholder: {%(value)s}') % {'value': e.args[0]})
 
         return JsonResponse({
             'item': preview_item,